Throughout the working life of a well, a number of units normally have to be installed and/or replaced. A plurality thereof are screwed into a well element. In order to release them, a tool is required which can grip and unscrew these units from engagement with the well element. An example of such an element is a valve which is located in the wellhead Christmas tree material, inside a gate valve, on an opening in the Christmas tree. In this case a tool has to grip the valve and unscrew it from engagement with the Christmas tree. During this process the tool will be exposed to the pressures under which the valve operates: the well pressure for the valve. This may be a casing pressure and/or other pressure in connection with the well.
The tool comprises a housing which is attached to the wellhead Christmas tree, and an internal element for unscrewing the valve from the Christmas tree must be rotated relative to the housing. This rotation gives rise to frictional forces, which are also partly dependent on the well pressure to which the tool is subjected. To carry out this rotation of the internal element places great demands on the system and with increasing force requirements, a larger force unit must be employed in order to achieve the desired rotation. This can be costly both with regard to production of the tool and during its use since the tool will also be heavier and therefore more difficult to handle. Thus there is a need for a tool where the rotation of the internal element is achieved with a relatively smaller tool.
The units which have to be installed or removed may often be difficult of access and the tool will normally have a telescopic function, where an inner movable element is moved in a telescopic function relative to the housing in order to become engaged with the unit and/or install/position the unit. If the distance between attachment point and engagement point is great, a possible solution is to make the tool as long as necessary in order to be able to carry out the activity. This results in a tool which may be difficult to handle and use on account of its great length. An alternative solution is to provide a telescopic function with several telescoping elements. A problem with such a telescopic member is to monitor where an outer end of the telescoping element is located. There is, moreover, also a need to retract the telescopic member into the housing so that the tool can be released. A simple solution is required here in order to achieve this.